Method and apparatus for continuously casting metals

ABSTRACT

Continuous casting of metal in which molten metal contacts a cooled axial mold wall surface to form a skin increasing in thickness in a direction toward a discharge opening of the mold. At least a portion of the last-mentioned mold surface increases in cross-sectional size over its length in the direction of the discharge opening. The casting is relatively withdrawn from the mold at an average casting rate during the casting operation and also the casting and the mold are oscillated relatively to one another in a particular manner. The maximum velocity capability of oscillation is greater than the casting rate. During oscillation and relative movement of the mold in the casting direction, a substantially constant, compressive loading of the last-mentioned mold surface portion on the skin of the casting is maintained throughout a portion of the last-mentioned movement. Concurrently with the relative movement of the mold in the casting direction, the resistance of the casting to mold movement is allowed to slow the mold velocity to approximately that of the casting, so as to minimize hot tearing of the skin of the casting.

[451 Dec. 31, 1974 METHOD AND APPARATUS FOR CONTINUOUSLY CASTING METALS ['75] Inventor: Leonard Watts, Cedarhurst, NY.

[73] Assignee: Technicon Instruments Corporation,

Tarrytown, NY.

[22] Filed: Mar. 22, 1973 [21] Appl. No.: 343,755

[52] US. Cl 164/83, 164/260, 164/281 [51] Int. Cl B22d 11/10 [58] Field of Search 164/83, 260, 281, 283 M [56] References Cited UNITED STATES PATENTS 2,135,183 ll/l938 Junghans 164/83 3,415,306 12/1968 Olsson 164/83 FOREIGN PATENTS OR APPLICATIONS 397,074 5/1962 Great Britain 164/66 935,046 8/1963 Great Britain 164/83 37,489 3/1906 Switzerland 164/283 M 440,570 12/ 1967 Switzerland 164/281 OTHER PUBLICATIONS Savage, A New Reciprocating Mould Cycle to Improve Surface Quality of Continuously Cast Steel, April 14, 1961, pp. l9. Scientific American, Vol. 209, No. 6, Dec. 1963, T 1.55, page 85.

Primary ExaminerR. Spencer Annear Attorney, Agent, or Firm-Stephen E. Rockwell; S. P. Tedesco [5 7] ABSTRACT Continuous casting of metal in which molten metal contacts a cooled axial mold wall surface to form a skin increasing in thickness in a direction toward a discharge opening of the mold. At least a portion of the last-mentioned mold surface increases in crosssectional size over its length in the direction of the discharge opening. The casting is relatively withdrawn from the mold at an average casting rate during the casting operation and also the casting and the mold are oscillated relatively to one another in a particular manner. The maximum velocity capability of oscillation is greater than the casting rate. During oscillation and relative movement of the mold in the casting direction, a substantially constant, compressive loading of the last-mentioned mold surface portion on the skin of the casting is maintained throughout a portion of the last-mentioned movement. Concurrently with the relative movement of the mold in the casting direction, the resistance of the casting to mold movement is allowed to slow the mold velocity to approximately that of the casting, so as to minimize hot tearing of the skin of the casting.

15 Claims, 5 Drawing Figures PATENTEDUEEMM 3.857.437

SHEET 10F 3 FIG.

PATENTED f3 857. 437 sum 3 [1F 5 METHOD AND APPARATUS FOR CONTINUOUSLY CASTING METALS BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates to a method and apparatus for continuous casting of metals, and relates more particularly to such method and apparatus which is improved to provide increased casting rates and smoother surface finish of castings.

2. Prior Art l-Ieretofore, casting rates have been restricted in part by inefficient dissipation of heat from continuous castings within cooled molds in which such castings are at least partially solidified to molded shapes. Such low heat dissipation has been caused by lack of effective cooling contact of such molds with solidifying castings therein.

The surface characteristics of castings made by prior art continuous casting techniques have also lacked desirable uniformity and smoothness due to hot tearing of the solidifying casting skin within such molds. Hot tearing results from resistance between the mold and thin solidifying skin upon movement of the casting relatively to the mold such as to create tensile stresses in the skin greater than the tensile strength of the skin. Hot tearing may also result in a phenomenon known as a breakout such as to cause cessation of the casting operation.

It is known that mold oscillation during continuous casting of metal is advantageous for minimizing local heat stresses in a casting mold, and such oscillation is shown and described, for example, in Junghans US. Pat. No. 2,135,183 issued Nov. 1, 1938. That patent describes in vertical casting apparatus reciprocating the mold in a special manner, namely so that the mold is moved a given distance in the casting direction at the same speed as the casting is withdrawn from the mold. Mold oscillation has also been utilized in horizontal continuous casting.

It is also known that in particular horizontal casting apparatus utilizing a stationary mold as shown and described in Webbere and Williams U.S. Pat. No. 3,642,058 issued Feb. 15, 1972, the mold may have a tubular internal axial surface portion provided with a taper opening in the casting direction to facilitate release of the casting by the mold on withdrawal of the casting, the taper being located adjoining a molten metal delivery nozzle. Oscillating molds have been known to have a similar taper but in an opposite direction and, at least in part, for approximating the cross sectional shrinkage of the casting on progressive longitudinal cooling of the casting within the mold in the casting direction. That is, the internal axial mold surface follows generally such shrinkage in an attempt to increase heat transfer between the casting and the mold in the area of the last-mentioned taper. The stationary mold of aforementioned U.S. Pat. No. 3,642,058 also is provided with a tapered surface portion of the lastmentioned type, located adjoining the first-mentioned taper and extending therefrom in the casting direction.

When a mold of the oscillating type such as described above is moved relatively to the casting in a direction opposite the casting direction, the thin solidifying skin of the casting in contact with the mold is placed in tension longitudinally which may result in hot tearing. On

the other hand, when the mold moves in the opposite direction, any pressure of the mold on the solidifying skin, such as to enhance heat transfer from the casting, is relieved. On the last-mentioned movement of the mold, the mold tends to lose contact with the casting skin unless hot tearing has previously occurred, and the tear has adhered to the mold.

The present invention includes the use of an oscillating mold in such casting of metals, which mold has a particular internal configuration throughout at least a portion thereof which, when the mold is oscillated, coacts with the casting forming within the mold to minimize hot tearing of the casting skin and maximize heat transfer from the casting.

SUMMARY OF THE INVENTION The invention contemplates improvement in techniques of continuous casting of metals, applicable to vertical and horizontal casting operations and casting operations utilizing molds of the open-ended type and of the type having a closed end or a plug. It contemplates improved cooperation between a molten metal delivery nozzle and an open-ended mold utilized in continuous casting of metals.

One object of the invention is to increase casting rates by improved cooling of a casting within and by a mold while at the same time improving the surface characteristics of such castings by effectively reducing hot tearing within a mold. Moreover the invention contemplates in this respect improved structure for healing any hot tearing.

Yet another object is to provide contact and axial compression between the mold and the thin solidifying skin of the casting on each movement of the mold in the casting direction during oscillation to repair any hot tearing and enhance heat transfer from the casting, while avoiding longitudinal tension on such skin such as to cause hot tearing on movement of the mold in the opposite direction.

Still another object is to allow the resistance of the casting to movement of the mold in the casting direction to slow the mold from a greater velocity to approximately the casting rate or velocity, and maintain substantially constant the axial pressure of the mold on the casting throughout a portion of the movement of the mold in the casting direction.

Among other objects of the invention which will be apparent from the following detailed description of the presently preferred forms of the invention are the continuous casting of metal in which molten metal contacts a cooled axial wall surface to form a skin increasing in thickness in a direction toward a discharge opening of the mold. At least a portion of the last-mentioned mold surface increases in cross-sectional size over its length in the direction of the discharge opening. The casting is relatively withdrawn from the mold at an average casting rate during the casting operation and also the casting and the mold are oscillated relatively to one another in a particular manner. The maximum velocity capability of oscillation is greater than the casting rate. During oscillation and relative movement of the mold in the casting direction, substantially constant, compressive loading of the last-mentioned surface portion on the skin of the casting is maintained throughout a portion of the last-mentioned movement. Concurrently with movement of the mold in the casting direction, resistance between the skin of the casting and the mold is allowed to slow the mold to approximately the velocity of the casting rate, so as to minimize hot tearing of the skin of the casting.

BRIEF DESCRIPTION OF THE DRAWINGS In the drawing:

FIG. 1 is a fragmentary schematic view of apparatus for continuous casting of metals, embodying the invention;

FIG. 2 is an enlarged broken and fragmentary view of the mold in cross section which may be employed in such apparatus and illustrates a particular internal surface configuration of a portion of the mold, omitting details of the water jacketing;

FIG. 3 is an enlarged median sectional view of the mold of FIG. I illustrating the latter in operation, omitting certain structural details of FIG. 1;

FIG. 4 is a fragmentary diagrammatic view illustrating certain parts of the mold oscillating mechanism in certain relative positions thereof during a typical oscillation cycle; and

FIG. 5 is a view similar to FIG. 4 but showing the parts in different relative positions during such an oscillation cycle.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS In the drawings, there is shown casting apparatus which is oriented horizontally for horizontal casting of metals but which may be used in a vertical orientation for a vertical casting if desired. In the form shown by way of example and with particular reference to FIGS. l and 3, a tundish, indicated generally at It), is provided for receipt, as from a non-illustrated ladle of molten metal to form a reservoir for such molten metal, having a refractory lining element 12 and a molten metal delivery tube or nozzle 14 also of a refractory material. As shown in FIG. 3, the discharge end of the nozzle 14 is surrounded by a copper collar 16 which is secured to the tundish as by being bolted thereto as at 18. The collar is provided with a passageway 20 for circulation therethrough of a coolant such as water. Intermediate a portion of the collar 16 and the discharge portion of the nozzle I4 is a sleeve 22 formed ofa heatresistance material such as boron nitride, for example, and which may have the cross-sectional configuration shown in FIG. 3. The sleeve 22 may be held in axially fixed relation to the collar 16 by suitable keys 24 and by abutment with the collar 16 in the manner shown. The sleeve 22 forms a continuation of the nozzle I4 for the discharge of molten metal.

The nozzle construction thus far described cooperates in this illustrated form with an open-ended mold 26 having in the wall structure thereof a passage 28 for the circulation of a coolant such as water therethrough and which mold is movable axially on oscillation with reference to the nozzle structure. In the illustrated form, the mold is slidingly supported on support element 30. The tundish may be supported in a conventional manner not shown. The cavity of the mold 26 has the desired cross-sectional shape of the casting to be produced. Suitable bearings 32 are interposed between the slidable mold 26 and the collar 16.

The forward end portion of the sleeve 22 of the nozzle structure which extends forwardly beyond the collar, has an outer peripheral surface 34 which is inclined in the manner shown to provide a cam surface for spring-biased sealing segments 36 interposed between the sleeve 22 and the mold 26 and spaced forwardly of the collar 16. The sealing segments 36, which are formed of a heat-resistant heat-resistant such as boron nitride or graphite coact internally with the mold and with one another around the interior of the mold for sealing purposes and each has a surface of complemental shape to the cam surface 34 for sliding engagement therewith so that the seal may move generally inwardly toward and outwardly from the center line of the mold. A plurality of compression springs are provided urging the sealing segments 36 outwardly against the mold, the springs being indicated at 38. Each spring 38 may have one end thereof socketed in the collar 16 and the other end thereof socketed in the corresponding sealing segment 36. The desired and selected maximum distance of oscillation of the mold in engagement with the seals 36 is represented by the solid line position and the broken line position of the mold shown in FIG. 3.

It is to be noted as shown in FIG. 3 that the seals 36 are located in the forward extremity of the tube or nozzle structure and in the positions shown form a continuation of the surface 40 of the sleeve 22. Owing to the construction and arrangement of the seals 36, the seals, which are spring biased, have a considerable forward and rearward component of movement capability on the cam surface 34 of the sleeve 22. The seals prevent the passage of molten metal rearwardly therepast while allowing hot gases from molten metal to pass and escape in the last-mentioned direction.

As indicated in FIG. 3 molten metal 42 from the tundish 10 exits therefrom into the mold 26 through the above-described nozzle structure in a manner such that the molten metal contacts the cooled internal axial surface of the mold and solidifies thereagainst to form a skin 44 which, as the casting operation proceeds, increases in thickness in the casting direction which is to the right as viewed in FIG. 3. The casting is indicated generally at 46. At the commencement of a casting operation, the usual dummy bar, inserted into the mold through the open end thereof remote from the tundish l0 and on which the molten metal solidifies, is withdrawn by the usual pinch rollers to commence the issuance of the casting from the mold. It will also be understood that the usual jets of cooling water are impinged on the casting along a portion of its length as it leaves the mold to solidify the casting further. The dummy bar, the pinch rollers and the water jets are not shown.

In accordance with the invention, the internal axial surface of the tubular wall structure of the mold is provided with an axial taper opening in the casting direction and located at least within the area of the internal axial surface which is exposed or in contact with the casting skin 44 where it is relatively thin and has little relative tensile strength, that is in an area where the skin is relatively newly formed. In the form illustrated by way of example in FIG. 2 the last-mentioned taper, indicated at 48, extends from the end of the mold which when the mold is assembled on the abovedescribed nozzle structure is closest to the tundish 10. When the mold is assembled in the last-mentioned manner the taper 48 extends in the casting direction beyond the nozzle structure, and the aforementioned seals 36 cooperate with the surface portion 48.

It is desirable that the taper 48 terminate in the casting direction a distance short of the discharge end of the mold, so that the internal axial surface of the mold may have forwardly and adjoining the taper 48 an axial surface portion which is untapered or which may have a taper converging in thhe casting the or a combination of such surface portions wherein the converging taper, not shown, is downstream of the untapered surface portion indicated at 50, to approximate the cross sectional shrinkage of the casting in the casting direction for better heat transfer from the casting in this area of the casting where the casting skin is relatively thick and strong as compared to the aforementioned thin portion of the skin 44.

The invention and the aforementioned configuration of the internal axial surface portion of the mold is applicable to the casting of metals utilizing a mold of the type having a closed end or mold cavity bottom as illustrated and described in my allowed co-pending U.S. patent application, Ser. No. 268,977, filed July 5, 1974, now U.S. Pat. No. 3,814,166, and in my U.S. Pat. No. 3,517,725 issued June 30, 1970, wherein the casting direction is in the direction toward the tundish from the mold. As shown and described therein the mold and the tundish are separated during a casting operation forming a casting having a solidified skin or shell around a molten core, and the mold and the casting are oscillated relatively to one another. Molten metal, flowing through the core of the casting and entering the mold cavity, enters the cavity adjacent the bottom thereof and forms a thin axial skin near the mold bottom which skin increases in thickness in the casting direction as the casting proceeds. The casting is withdrawn from the mold by solidification on a starting device supported on the tundish. For the purpose of describing and claiming the invention as applied to the casting of metals utilizing a mold of the closed end type, the molten metal inlet of the mold is considered as distinct and separate from the open discharge end of the mold. The molten metal inlet is considered as being adjacent the bottom of the mold within the mold cavity.

With reference to the oscillation of the mold, the mold has a maximum velocity capability in the casting or forward direction which is greater than the casting rate. The mold velocity in the forward direction is the sum of the casting rate, the component due to deformation of the casting by the mold and longitudinal shrinkage of the casting. Another feature of the mold oscillation is that the casting, during such forward movement, slows the mold to approximately the casting rate or velocity by the resistance of the skin of the casting to movement of the mold. Various devices or mechanisms such as an air cylinder may be utilized for accomplishment of these features. For example, limit switches may be utilized to fix the length of the stroke. However, the presently preferred oscillation mechanism, one form of which is illustrated, utilizes, instead of an air cylinder, a driver for the mold which is in the form of a timed cam or crank. Further, the maximum compressive load of the mold on the skin of the casting lengthwise of the latter is predetermined during any portion of a cast and may be adjusted during the cast. In addition, such compressive loading on the skin may be maintained substantially constant throughout a portion of the forward stroke of the mold.

The general organization of the drive for oscillating the mold is shown diagrammatically in FIG. 1, wherein a cam or crankwheel 52 is driven through suitable reduction gearing from a prime mover 54. A link, indicated generally at 56, self-adjusting as to length, interconnects the cam or crankwheel 52 with a flange 58 in fixed relation to the mold 26. In the form shown, the driving wheel 52 generates a sine wave but the wheel 52 may be so constructed as to generate other wave forms. In the form shown for illustrative purposes only, one end of the link 56 is pivoted (FIGS. 4 and 5) eccentrically to the wheel 52 as at 60. The other end of the link 56 is pivoted to the flange 58 of the mold as at 62. The motor 54, which is of the adjustable speed type, drives the wheel 52 at a predetermined constant speed.

The link 56, best shown in FIGS. 4 and 5, includes a pneumatic cylinder 64 having at one end thereof a rod extension 66 fixed to the cylinder 64. The distal end of the rod 66 has the aforementioned pivot connection 60 to the wheel 52. The link 56 also includes a driven member in the form of piston 68 in the cylinder 64, provided with a piston rod 70 having the aforementioned pivot connection 62 with the flange 58 of the mold. A source of compressed gas, not shown, has an output 72 to a pressure regulator 74 and a gas line 76 connects the cylinder 64 and the regulator 74. The pressure regulator 74, which is of a conventional type, not only governs the input to the cylinder 64 through the line 76 but has the function of relieving pressure in the cylinder 64 through the line 76 to maintain a con stant pressure therein regardless of the position of the piston 68 in the cylinder. Hence, gas line 76 is a twoway gas line.

The cylinder 64 and' piston 68 form a constant-rate air spring, the pressure of which is adjustable by the regulator 74. It will be understood that the torque of the wheel 52 is greater than the maximum anticipated desired loading of the air spring. The load of the air spring represents the maximum load with which the mold 26 is moved in the forward direction, and may be changed during the casting operation to accommodate changing thermal conditions in the mold if desired. The compressive loading of the mold on the forward stroke is always sufficient to maintain intimate contact between the mold taper 48 and the casting for heat transfer from the latter. The load on the mold may also be adjusted in accordance with the particular metal being cast.

During the early part of a casting operation, owing to thermal conditions in the mold, the casting skin may be relatively thin and weak and require less of a load than during a later part of the casting operation as when the temperature of the metal being poured has decreased by the amount of superheat lost as during the pouring of molten metal from a ladle into the tundish over a period of time, say 1 hour for example. Upon such a reduction in the superheat in the metal, the molten metal may solidify faster in the formation of the casting skin.

The speed of the forward oscillation stroke is in part always greater per unit length than the casting rate at the same unit length. The difference may not be significant, but if operating conditions require it, the difference may be substantial. As is customary, the speed or rate of withdrawal of the casting from the mold is adjustable and, as previously indicated the speed of the driving wheel 52 may be adjusted by adjusting the speed of the motor 54. Usually the proportional difference between the forward oscillation stroke of the mold and the withdrawal rate of the casting is maintained throughout a casting operation. That is, when the casting speed is increased during a casting operation, the speed of the driving wheel 52 is increased correspondingly.

As has been made clear, the compressive load of the mold on the casting is through the taper &8 of the mold bearing on the skin of the casting during the forward stroke, and the load is relieved on the rearward stroke. The cam or crankwheel 52 rotates in the direction of the arrow of FIGS. 4 and 5, and at the instant in time in which the pivot 60 is in the position of FIG. 4, the mold is at rest, the mold having been returned to the fullest extent of its rearward movement from a forward position by the pull of the cylinder 64 on the piston 68.

At the commencement of the forward stroke, that is from the position of the pivot 6t) of FIG. 4 moving toward the position of the pivot 60 of FIG. 5, the mold accelerates in the forward direction and catches up to the speed of the casting rate. It may pass the speed of the casting rate on acceleration, provided that the skin of the casting in contact with the taper 48 of the mold is sufficiently soft to be deformed by the mold, as the pivot 60 approaches the position of FIG. 5 from the position of FIG. 4. If the casting skin, as the mold travels thereover, is sufficiently soft to be deformed by the compressive loading on the casting skin throughout the entire area of the skin which is contacted by the mold taper 48, the mold may travel to its fullest extent in a forward direction, with the piston 68 remaining in the cylinder-bottoming position of FIG. 4.

However, the resistance of the casting skin to movement of the mold in a forward direction is usually such as to be greater than the compressive loading on the casting dictated by the air pressure in the cylinder 64, and this condition is shown in FIG. 5. During the angular movement of the driving wheel 52 from the position of FIG. 4 to that of FIG. 5, the resistance of the casting to the mold movement has slowed the velocity of the mold to approximately that of the casting rate, and accordingly the piston 68 is displaced to the extent shown by way of example in FIG. 5. When the mold is slowed to the casting rate in this manner, the compressive loading on the casting remains substantially constant through a portion of the forward mold stroke.

Because of the action of the air spring formed by the cylinder 6 and the piston 68, the mold taper 48 may remain in contact with the casting for a period of time after the velocity component of the cam on the forward stroke has slowed to a speed below that of the casting, as the driving wheel 52 rotates from the angular position of FIG. 5 through a further angle in a clockwise direction thereof. Thus, the action of the air spring, when the piston 68 has been displaced in the cylinder 64 by resistance of the casting to mold movement, is such as to attempt to effect the maximum forward stroke of the mold.

It is to be noted that the length of the forward stroke during an oscillation cycle is dependent upon the relative velocities of the casting and the mold and the resistance of the casting to the mold movement. Further, it is made clear from the foregoing that the casting, through its resistance to mold movement on the forward stroke, itself changes the character of mold oscillation during a casting operation such as average mold velocity on the last-mentioned stroke, effectively tending to achieve a character of mold oscillation suitable to the then prevailing particular conditions of the casting operation including thermal conditions. During changing thermal conditions of a casting operation, the maximum compressive loading of the mold on the casting will remain constant, provided that the regulated air pressure in the cylinder 64 is not adjusted by the regulator 74.

While the mold taper 48 is in contact with the relatively thin skin of the casting there is substantial heat transfer from the casting. This improved cooling of a casting within and by the mold makes possible an increase in casting rates while at the same time improving the surface characteristics of such casting by effectively reducing hot tearing within the mold. Further, the remaining objects of the invention are achieved.

While several preferred embodiments of the invention have been described, it will be apparent especially to those versed in the art that the invention may take other forms and is susceptible of various changes in details without departure from the principles of the invention.

What is claimed is:

1. A process of continuously casting an elongated metal article, utilizing a mold having a molten metal inlet, a cooled tubular wall structure and an open outlet end for the issuance of a casting therefrom in at least partially solidified form, and comprising the steps of:

introducing molten metal into said mold from a source for contact and solidification against said wall structure to form a casting skin which increases in thickness in the direction of said mold outlet as the casting is relatively moved along the mold in the casting direction;

relatively withdrawing the casting from the mold at the open outlet end continuously at an average casting rate;

oscillating said mold relatively to the casting for movement forwardly in the casting direction and rearwardly, at least a portion of said forward mold movement being faster than said casting rate; and

compressing the casting skin axially and radially inwardly by the mold during each forward movement of the mold for enhanced thermal transfer from the casting.

2. A method as defined in claim 1, further including, maintaining a predetermined compressive loading of said mold on said casting skin substantially constant throughout a portion of said mold forward movement.

3. A method as defined in claim 1, wherein: said mold is substantially vertically arranged and said relative withdrawal of said casting from said mold has a substantial vertical movement.

4. A method as defined in claim I, wherein: said mold is substantially horizontally arranged and said relative withdrawal of said casting from said mold has a substantial horizontal movement.

5. A method as defined in claim 1, wherein: said mold is open-ended and said molten metal is introduced into the open end of said mold remote from said outlet end.

6. A method as defined in claim 1, wherein: said mold defines a mold cavity having a closed end remote from said metal source forming a bottom of said cavity, said open outlet end of said mold opening toward said metal source, said mold and said source being separated during relative withdrawal of the casting from the mold, the casting direction being from said mold toward said source, the casting skin forming a solidified shell around a molten core through which core molten metal flows to said mold from said source, said molten metal being introduced into said mold cavity adjacent the bottom thereof.

7. A method as defined in claim 1, wherein: said metal which is cast is steel.

8. A method as defined in claim 1, wherein: said oscillation of the mold relatively to the casting is at a fixed frequency for an oscillation cycle.

9. A method as defined in claim 1 wherein: the distance of travel of the mold in the forward direction during an oscillation cycle is dependent upon the relative velocities of the casting rate and the forward movement of the mold and the resistance of the casting to mold movement.

10. Apparatus for continuously casting an elongated metal article, comprising: a mold having a molten metal inlet in communication with a source of molten metal and having a cooled tubular wall structure and an open outlet end for issuance of a casting therefrom in at least partially solidified form, said wall structure having an internal surface area against which the molten metal has contact and forms a skin increasing in thickness in a direction toward said mold outlet end as the casting is relatively moved along the mold in a casting direction, said wall structure having in said area a surface portion gradually increasing in cross sectional size in the direction of said mold outlet end for contact with and thermal transfer from the casting in the area of the latter initially undergoing solidification, means relatively withdrawing the casting continuously from said mold, and an oscillating device oscillating said mold relatively to the casting for movement of the former forwardly in the casting direction and rearwardly in the opposite direction, at least a portion of said forward mold movement being faster than the rate at which the casting is relatively withdrawn from the mold.

11. Apparatus as defined in claim 10, wherein: said oscillation device comprises means exerting a substantially constant, predetermined compressive loading of said mold on said casting skin portion throughout a portion of said mold movement.

12. Apparatus as defined in claim 10, wherein: said mold is open-ended and said molten metal inlet is formed by the open end of the mold remote from the open discharge end of the mold.

13. Apparatus as defined in claim 10, wherein: said mold defines a mold cavity having a closed end remote from said metal source forming a bottom of said cavity, said open outlet end of said mold opening toward said metal source, said mold in said source being separated during relative withdrawal of the casting from the mold, the casting direction being from said mold toward said source, the casting skin forming a solidified shell around the molten core through which core molten metal flows to said mold from said source.

14. Apparatus as defined in claim 10, wherein: said oscillation device comprises means of oscillating said mold relatively to the casting at a fixed frequency for an oscillation cycle.

15. Apparatus as defined in claim 10, wherein: the distance of travel of the mold in the forward direction during an oscillation cycle is dependent upon the relative velocities of the casting rate and the forward movement of the mold and the resistance of the casting to such forward mold movement. 

1. A process of continuously casting an elongated metal article, utilizing a mold having a molten metal inlet, a cooled tubular wall structure and an open outlet end for the issuance of a casting therefrom in at least partially solidified form, and comprising the steps of: introducing molten metal into said mold from a source for contact and solidification against said wall structure to form a casting skin which increases in thickness in the direction of said mold outlet as the casting is relatively moved along the mold in the casting direction; relatively withdrawing the casting from the mold at the open outlet end continuously at an average casting rate; oscillating said mold relatively to the casting for movement forwardly in the casting direction and rearwardly, at least a portion of said forward mold movement being faster than said casting rate; and compressing the casting skin aXially and radially inwardly by the mold during each forward movement of the mold for enhanced thermal transfer from the casting.
 2. A method as defined in claim 1, further including, maintaining a predetermined compressive loading of said mold on said casting skin substantially constant throughout a portion of said mold forward movement.
 3. A method as defined in claim 1, wherein: said mold is substantially vertically arranged and said relative withdrawal of said casting from said mold has a substantial vertical movement.
 4. A method as defined in claim 1, wherein: said mold is substantially horizontally arranged and said relative withdrawal of said casting from said mold has a substantial horizontal movement.
 5. A method as defined in claim 1, wherein: said mold is open-ended and said molten metal is introduced into the open end of said mold remote from said outlet end.
 6. A method as defined in claim 1, wherein: said mold defines a mold cavity having a closed end remote from said metal source forming a bottom of said cavity, said open outlet end of said mold opening toward said metal source, said mold and said source being separated during relative withdrawal of the casting from the mold, the casting direction being from said mold toward said source, the casting skin forming a solidified shell around a molten core through which core molten metal flows to said mold from said source, said molten metal being introduced into said mold cavity adjacent the bottom thereof.
 7. A method as defined in claim 1, wherein: said metal which is cast is steel.
 8. A method as defined in claim 1, wherein: said oscillation of the mold relatively to the casting is at a fixed frequency for an oscillation cycle.
 9. A method as defined in claim 1 wherein: the distance of travel of the mold in the forward direction during an oscillation cycle is dependent upon the relative velocities of the casting rate and the forward movement of the mold and the resistance of the casting to mold movement.
 11. Apparatus as defined in claim 10, wherein: said oscillation device comprises means exerting a substantially constant, predetermined compressive loading of said mold on said casting skin portion throughout a portion of said mold movement.
 12. Apparatus as defined in claim 10, wherein: said mold is open-ended and said molten metal inlet is formed by the open end of the mold remote from the open discharge end of the mold.
 13. Apparatus as defined in claim 10, wherein: said mold defines a mold cavity having a closed end remote from said metal source forming a bottom of said cavity, said open outlet end of said mold opening toward said metal source, said mold in said source being separated during relative withdrawal of the casting from the mold, the casting direction being from said mold toward said source, the casting skin forming a solidified shell around the molten core through which core molten metal flows to said mold from said source.
 14. Apparatus as defined in claim 10, wherein: said oscillation device comprises means of oscillating said mold relatively to the casting at a fixed frequency for an oscillation cycle.
 15. Apparatus as defined in claim 10, wherein: the distance of travel of the mold in the forward direction during an oscillation cycle is dependent upon the relative velocities of the casting rate and the forward movement of the mold and the resistance of the casting to such forward mold movement. 